$\sin(-\frac{2}{3}\pi) = \text{?}$
Explanation: To find the sine using the unit circle, first find the angle. Drag the orange point around the circle until $-\frac{2}{3}\pi$ is selected. The correct angle is selected. Remember, the sine of an angle is represented by the $y$ coordinate of a point on the unit circle. The $y$ coordinate of the point is $-0.866$, so $\sin(-\frac{2}{3}\pi) = -0.866$.